The present invention is directed to an underwater spear gun of the surgical-band, or sling, type. Conventional spear guns may be classified according to two general types: The pneumatic spear gun, which utilizes an air-driven, piston to drive the spear shaft down a rifle-like barrel; and a rubber-powered, or sling-type, spear gun, in which one or more rubber bands propel the spear shaft after trigger. The first type of spear gun--the pneumatic--is advantageous in that it is a relatively accurate device, allowing accurate aiming of the spear. However, it is disadvantageous since the power to drive the spear shaft is limited by the physical strength of the user of the gun, since, during loading, the air is further compressed and the piston set by the diver himself. The only way to increase the power of such a spear gun is to increase the initial pressure of the compressed air. If such initial pressure were to be too great, the diver would not be able overcome it during each loading. Thus, each pneumatic spear gun has a limit to the maximum power output thereof, which also is directly dependent upon the diver's strength. In contradistinction, the advantage of the rubber-powered spear gun is the ability for greater power input, and, therefore, allows greater spear-shaft speeds. However, the disadvantage is the poor aiming accuracy associated therewith. The enhanced power input derives from the fact that one or more individual rubber bands may be used to power the spear shaft, the total power input being the sum of the individual bands. Since the maximum strength required for a diver to load such a spear gun is only his ability to stretch and load one rubber band, the power input is not limited by the diver's strength, since he may load a plurality of such rubber bands, each band being loaded independently of the others, and each requiring the same amount of effort on the part of the diver. Thus, loading two such rubber bands will double the power input relative to one rubber band, with each band being loaded by the diver requiring the same load-effort. However, since the barrel of the spear gun for such rubber-powered types must be exposed along its length for approximately 180 degrees about the circumference thereof, accuracy is sacrificed, since upon the triggering of the device, the rearward-end of the spear shaft is caused up-and-down oscillation as each rubber band shortens in length during firing. That is to say, the more rubber bands used, the greater the power output for the spear-shaft, which additional force, however, leads to the bowing of the spear-shaft proper, thus reducing aiming accuracy. Tests have shown that after launching of the spear, the tip of the spear remains relatively stationary to the spear-shaft proper, which, as mentioned above, oscillates.